It is desirable and known, in certain applications, to connect one terminal of a miniature permanent magnet d.c. motor to the motor's housing or casing. One such application is in small battery operated devices such as a shaver or hand held personal fan where one of the spring contacts, for the battery also contacts the motor casing, eliminating the need for a wire and a connector to connect the battery to one terminal. The other terminal is connected to the other battery contact by a wire and connector via a switch or other motor control device. Thus this arrangement, by eliminating one wire and connector, represents a significant saving in the overall cost of the device.
One known method of connecting the terminal to the casing is by a small strip of conductive sheet metal, usually brass, being spot welded to the terminal and the casing. The advantage of this is that the earth strap is added after the motor has been completely assembled allowing stocks of motors to be produced for various applications and only earthed for specific applications once known or ordered. Another advantage is that the earth strap can be easily seen and thus any missing straps are readily identified and rejected during visual inspection. A disadvantage is that the spot welding of the earth strap can only be done once the motor has been assembled, and there is a danger of the welding current affecting the magnets fitted inside the motor casing. Also, the spot welding is relatively weak and as the earth strap is on the outside of the casing, it is subject to knocks during shipping and assembly which could crack the spot weld joint creating a bad or weak electrical contact leading to a defective device. Such bad joints are difficult to spot visually unless the joint is completely broken, in which case the strap may be missing altogether.
Today's trend to avoid stockpiling of motors, as highlighted by the "just-in-time" manufacturing methodology, means that the advantage of post assembly addition of the earth strap is no longer a real advantage.
Thus, it is an object of the present invention to provide a motor with an earth strap which is readily identified by visual inspection, but is unlikely to be dislodged or damaged by rough handling during shipping or fitting into an appliance.